David Byrne and Brian Eno have collaborated for an album called Everything That Happens Will Happen Today. Here's the site where you can download the MP3 (via email link) and check out the tour dates! Maybe I'll see you at the Boston show.
Radiohead is streaming a webcast which they are calling "Thumbs Down" as we speak at Radiohead.tv. So far it's been Radiohead performing, someone spinning music to strange moving and still images, and footage of everyone just sitting around a table. I think the performances are live, though I have not been able to find the exact details online.
From what I've read, they did a live 'testcast' last night and performed Bjork's Unravel (see below). I've had a lot of fun watching it so far.
UPDATE: Right now they are playing one of my favorite songs: Umbabarauma by Ponta de Lanca Africano. This is a lot of fun!
UPDATE 2: I do think this is live as Thom just came on and talked about it a bit. It's almost like they are hosting a variety show. They're now playing a video for "Jigsaw Falling Into Place" from their new album.